1. Field of the Invention
The present invention relates to an electrode forming apparatus for applying electrode paste onto ends of chip type electronic components. More particularly, the invention relates to an apparatus for forming electrodes of uniform width and thickness by spreading the electrode paste uniformly over the bottom of a dipping vessel used to apply the paste to the chip type electronic components.
2. Description of the Background Art
In general a holding plate having a number of receiving holes is employed for efficiently applying electrodes to end portions of a number of chip type electronic components, as disclosed in U.S. Pat. No. 4,395,184. This holding plate comprises a hard substrate, a thin flat plate portion which is formed at a central portion of the substrate, provided with a number of through holes, and a rubber-like elastic member which is embedded in a concave portion defined in the flat plate portion. The rubber-like elastic member is provided with receiving holes, passing through the elastic member, which are smaller in diameter than the through holes provided in the thin plate portion. The holding plate elastically holds chip type electronic components in the receiving holes so that the components partially project from the holding plate, and electrode paste of silver or the like is uniformly applied to the projected portions. Thereafter, the chip type electronic components are heated to dry the electrode paste.
The aforementioned U.S. Patent describes an exemplary method of applying electrode paste to such chip type electronic components with a roller. In this method, a holding plate holding chip type electronic components which partially project from its upper surface is carried by a conveyor. A roller which is coated with electrode paste on its peripheral surface is brought into contact with the projecting portions of the chip type electronic components to apply the electrode paste onto the chip type electronic components. In order to obtain uniform thickness of the paste around the peripheral surface of the roller, a scraper is employed for scraping off the excess part of the paste while rotating the roller.
When the chip type electronic components are about 1.6 to 5.7 mm in length, for example, the electrodes have extremely small thickness, ranging from about 0.15 to 0.3 mm, which must be controlled with high accuracy. In the aforementioned method, however, the paste which is applied to the peripheral surface of the roller flows, following the rotation of the peripheral surface, and hence the thickness of the paste varies to cause variation in thickness of the electrodes which are formed on the chip type electronic components. Such variation may also be caused by vibration of the conveyor or fluctuation in the degree of horizontalness of the apparatus.
Japanese Patent Publication No. 3-44404 (1991) describes a method of coating the upper surface of a flat coating plate with a thin film of electrode paste. A holding plate, holding chip type electronic components so that they partially project downwards, approaches the coating plate, thereby pressing the projected portions of the chip type electronic components against the coating plate to apply the electrode paste to the chip type electronic components. This method avoids the problems encountered in the aforementioned method employing a roller. According to this method, the projecting portions of the chip type electronic components are pressed against the bottom surface of the coating plate which is coated with the paste. This method prevents variation in length of projecting portions and provides uniform electrode thickness.
When a single application step is completed, however, the paste film is reduced in thickness in portions applied to the chip type electronic components. Therefore, it is necessary to temporarily collect the paste remaining on the coating plate to re-adjust the same to a constant thickness. Thus, much time is required for adjusting the film thickness and it is difficult to adjust the paste film to a constant thickness with high repeatability.